Why is Earth geologically active? Internal heat drives geological activity, and Earth retains internal heat because of its relatively large size for a terrestrial world. This heat causes mantle convection and keeps Earth's lithosphere thin, ensuring active surface geology. It also keeps part of Earth's core melted, and circulation of this molten metal creates Earth's magnetic field.
What processes shape Earth's surface?
- Impact cratering
- Volcanism
- Tectonics
- Erosion
Earth has experienced many impacts, but most craters have been erased by other processes. We owe the existence of our atmosphere and oceans to volcanic outgassing. A special type of tectonics, plate tectonics, shapes much of Earth's surface. Ice, water, and wind drive rampant erosion on our planet.
How does Earth's atmosphere affect the planet? Two crucial effects are protecting the surface from dangerous solar radiation, UV is absorbed by ozone and X rays are absorbed high in the atmosphere, and the greenhouse effect, without which the surface temperature would be below freezing.
Was there ever geological activity on the Moon or Mercury? Both the Moon and Mercury had some volcanism and tectonics when they were young. However, because of their small sizes, their interiors long ago cooled too much for ongoing geological activity.
What geological features tell us that water once flowed on Mars? Dry riverbeds, eroded craters, and chemical analysis of Martian rocks all show that water once flowed on Mars, though any periods of rainfall seem to have ended at least 3 billion years ago. Mars today still has water ice underground and in its polar caps and could possibly have pockets of underground liquid water.
Why did Mars change? Mars' atmosphere must once have been thicker with a stronger greenhouse effect, so change must have occurred due to loss of atmospheric gas. Much of the lost gas probably was stripped away by the solar wind, after Mars lost its magnetic field and protective magnetosphere. Mars also lost water, because solar ultraviolet light split water molecules apart and the hydrogen escaped to space.
Is Venus geologically active? Venus almost certainly remains geologically active today. Its surface shows evidence of major volcanic or tectonic activity in the past billion years, and it should retain nearly as much internal heat as Earth. However, geological activity on Venus differs from that on Earth in at least two key ways: lack of erosion and lack of plate tectonics.
Why is Venus so hot? Venus' extreme surface heat is a result of its thick, carbon dioxide atmosphere, which creates a very strong greenhouse effect. The reason Venus has such a thick atmosphere is its distance from the Sun: it was too close to develop liquid oceans like those on Earth, where most of the outgassed carbon dioxide dissolved in water and became locked away in carbonate rock. Carbon dioxide remained in Venus' atmosphere, creating a runaway greenhouse effect.
What unique features of Earth are important for life?
- surface liquid water, made possible by Earth's moderate temperature
- atmospheric oxygen, a produce of photosynthetic life
- plate tectonics, driven by internal heat
- climate stability, a result of the carbon dioxide cycle, which in turn requires plate tectonics
How is human activity changing our planet? The global average temperature has risen about .8 degrees Celsius over the past hundred years, accompanied by an even larger rise in the atmospheric CO2 concentration, a result of fossil fuel burning and other human activity. The current CO2 concentration is higher than at any time in the past million years, and climate models indicate that this higher concentration is indeed the cause of global warming.
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Good work.
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